1. Field of the Invention
The present invention relates to a colored plastic lens and method of manufacturing therefor, and more particularly to a colored plastic lens which does not discolor during application of a surface hardening film.
2. Description of the Related Art
Plastic lenses have the characteristics of being easy to mold, light- and crack-resistant, and easy to color with dyes, so they have become widely used in recent years as optical lenses, and especially as optical lenses for eyeglasses. The advantage of being able to easily color plastic lenses with dyes is especially important for eyeglass fashionability and shading. It has been estimated that at least 70% of the plastic eyeglass lenses on the market are dyed. That being the case, there is an emerging need for a high-volume dyeing method which yields uniform, consistent color as well as a large variety of colors. The most commonly used method for dyeing plastic lenses is the so-called dip-dyeing method. According to this method, a dye solution is prepared in which dye is dispersed in a water/surface active agent solution. The plastic lens is dipped in the dye solution while being heated. As an alternative to the aforementioned dip-dyeing method, a method of sublimating an organic pigment to color plastic lenses is proposed in Japanese Patent Publication 35-1384. As another alternative, a method of sublimating a sublimating dye to color plastic lenses is proposed in Japanese Patent Publication 56-153321, Japanese Patent Publication 56-159376, and Japanese Patent Publication 1-277814.
Because the surface hardness of an unmodified plastic lens is insufficient, there are disadvantages in that the lens is easily scratched and surface reflection develops due to the flickering of images and solid objects. To improve surface hardness, a silicon-based hard coat film is applied to the lens base material, and in order to improve surface reflection, inorganic substances are vapor-deposited on the surface of the lens to create a reflection-preventing film. However, using silicon-based hard coat films and inorganic reflection-preventing films reduces the impact resistance of the plastic lens.
To improve the impact resistance of the plastic lens, it is necessary to improve the surface by placing a primer layer between the lens base material and the silicon-based hard coat film. As an example of this method, it has been proposed to use an epoxy resin as the primer composite (Japanese Patent Publication 60-214301). Alternatively, it has been proposed to use an acrylic polyol and a multi-functional organic isocyanate compound as the primer composite (Japanese Patent Publication 61-114203).
In the method of dipping in a dye solution, which is the conventional method of dyeing plastic lenses, there tend to be great variations in color tone. These are the result of variations in the concentration of the dispersed dye in the dye solution, the amount of dyeing auxiliaries, the temperature of the dye solution, and the dye affinity of the plastic lens base material. It is thus difficult to obtain uniform and consistent dyed plastic lenses in large quantities using the dip-dyeing method.
Moreover, because the vapor phase dyeing methods disclosed in Japanese Patent Publication 56-153321 and Japanese Patent Publication 56-159376 use solid dye-affinity dyes or block-type solid dyes, there are problems in that the dye may not be uniformly heated on the lens surface. Also according to the vapor phase dyeing methods, it is difficult to adjust the dye concentration. With the dyeing method disclosed in Japanese Patent Publication 1-277814, it is necessary to prepare a vacuum environment.
In addition to the above-mentioned problems, the dye is positioned on the surface of the plastic lens in the form of molecules. Thus, plastic lenses which have been dyed by the dip-dyeing method or the vapor phase dyeing method have problems with light resistance and weather resistance. Discoloration and decoloration occur when the dyed lenses are used for long periods of time and struck by strong sunlight in the summer and by ultraviolet rays reflected off of snow in the winter.
On the other hand, in the coloring by the pigment method described in Japanese Patent Publication 35-1384, there are problems in terms of operability. In this method, a vacuum environment is necessary and a treatment temperature of 150-200.degree. C. is used. This creates a danger in that the plastic lens itself will be penetrated, resulting in a loss of optical performance.
When a primer layer is put on a lens which has been dyed by the dipping method and a silicon-based hard coat film is applied on top of the primer layer through dipping, the dyed lens is dipped in hardening solution. The problem with this method is that the dye applied to the lens exudes out into the hardening solution, and this causes the hardening solution to become colored. When subsequent dipping is performed using the same hardening solution, other lenses may become colored by the hardening solution. Thus, a difference develops in the originally-dyed color tone after the hardening process.